This invention relates to polyoxazolidone polymers and a process for preparing same. More particularly, this invention relates to polyoxazolidone polymers containing relatively small proportions of trimerized polyisocyanates.
It is well known to react an epoxide with an isocyanate to form an oxazolidone. Such reactions are generally carried out in the presence of a catalyst. Typical catalysts for this reaction include lithium bromide, quaternary ammonium salts, tertiary amines, Lewis acids, such as aluminum chloride, complexes of these Lewis acids with a Lewis base, and similar materials.
In similar manner, polyoxazolidone polymers can be prepared by reacting a diepoxide (i.e. a compound having at least two oxirane groups) with a polyisocyanate (i.e. a compound having at least two isocyanate groups). However, whereas the reaction of a monoepoxide and a monoisocyanate to form an oxazolidone proceeds relatively cleanly and in good yield, the corresponding reaction between higher functionality epoxides and isocyanates results in the formation of substantial quantities of undesirable byproducts. The major by-products are polyethers prepared by the homopolymerization of the polyepoxide and isocyanurates formed by the trimerization of the polyisocyanate. Of these, the trimerization reaction is particularly disadvantageous since the trimerization leads to the formation of very high functionality materials which give rise to very highly crosslinked, brittle polymers. Unfortunately, the catalysts conventionally used in preparing polyoxazolidones do not selectively catalyze the oxazolidone reaction, and substantial quantities of isocyanurates are formed. Generally, the polyoxazolidone contains about 20 to 40 mole percent or more of isocyanurates.
For this reason, it would be desirable to provide a process whereby a polyepoxide and polyisocyanate are reacted to form a polyoxazolidone polymer containing relatively small quantities of trimerized isocyanates.